In recent decades, astronomers have believed that invisible, mysterious dark matter is the dominant aspect of any galaxy. Astronomers consider dark matter to be galaxies. That's why they are so surprised to find a galaxy with no (or very little) dark matter. The discovery challenges astronomers' ideas about the formation of galaxies. A research team led by Yale made the discovery while looking into the distant galaxy NGC 1052-DF2. These astronomers say that their discovery has far-reaching implications for our understanding of the universe. A statement by Yale dated March 28, 2018 said:
It shows for the first time that dark matter is not always associated with galactic-scale traditional matter …
Yale's astronomer Pieter van Dokkum is lead author the new study published in the journal Nature . He said:
We thought that every galaxy has dark matter and that dark matter is a galaxy.
To make this discovery, the team used a telescope that was invented by van Dokkum and built together with co-author Roberto Abraham, the University of Toronto. It's called Dragonfly Tele Array. The galaxy had previously been cataloged, but these researchers said they had noticed that the dragonfly images looked very different. Co-author Shany Danieli, a Yale student, commented:
It looked like a diffused blob speckled with very compact star clusters. I love working with the Dragonfly Telescope because it shows us weak structures that nobody has ever seen before.
The researchers then used the W.M. Keck Observatory in Hawaii to measure the movements of 10 very dense groupings of stars called globular clusters that orbit the center of this galaxy. They found that the clusters moved at relatively slow speeds – less than 23,000 miles (37,000 km) per hour. Stars in dark matter galaxies move at least three times faster. Van Dokkum explained that the researchers used the new motion measurements to calculate the mass of NGC 1052-DF2. At that time, they discovered that this galaxy is very different from other galaxies. Van Dokkum said:
If there is dark matter at all, it is very little. The stars in the galaxy can be responsible for the entire mass, and there seems to be no room for dark matter.
I spent an hour looking at the Hubble image. It's so rare, especially in those days after so many years of Hubble, that you get a picture of something and say, "I've never seen that before." This thing is amazing, a huge blob that you can see through. It is so sparse that you can see all the galaxies behind it. It's literally a translucent galaxy. Bottom line: The galaxy NGC 1052-DF2 does not seem to have any dark matter. It confuses astronomers theories of the universe, stating that galaxies need dark matter to form.
Source: A galaxy without dark matter